Small amount of blood found in bedding

This is my first time breeding mice for bare with me, please.

I have 2 mice that are breeding and I don't know the age of either of them because local pet stores don't keep track of that. I had 6 mice and there was only one female out of all of them, so I put her with a male and I was told to wait 16 days, take the male out, and hope she's pregnant. The first day they were just settling in, but a few hours later the male started to go for her. He tried a lot but she squeaked at him and he backed off. I read that she squeaks because she's in heat but she's not ready. But he toned it down the second day, but still tried. She still resisted. But I noticed that in their small igloo, I think it's the girl that's kicking up aspen bedding to make a deeper hole and bringing some back in. They both sleep in there now but I was wondering if that was nesting or just mice burrowing because they want to hide.

Anyway, it's the third day and they're both usually in the igloo, curled up together. And they'll occasionally come out for food, water, and to run on the wheel. But I picked up the igloo because I was curious about why they dug into the igloo and all I saw were two aspen chips stained with blood. I don't know who bled but they both seem healthy. I checked both of them and there were no stains of blood or anything. I noticed the female's genitals seemed wet, if that says anything.

I don't know what this is and I don't know if it was the male being too forceful when he tried to go at her or if this is some internal bleeding. I'll check tomorrow to see if there's more but there's not too much.

Thanks. (All my mice are albino feeder mice)

She is either about to have babies or has had them and they were eaten. Check again later and see if there are any pinkies or more blood. You may also find pinky parts if they have eaten the babies. It's not uncommon for a first litter to be eaten, but if it happens a second time get new mice.

Being with a male for three days wont produce any baby mice yet. When ANY mice, female or male are introduced to each other they will fight. Usually to assert dominance or because they smell different and are not used to each other. Mice a territorial and will kill each other if their territory is breached. Males will fight no matter what and they will fight to the death. Females are a lot easier to place together.

I highly doubt that the first time you introduced these two that they were breeding. They were fighting. If the female mouse was squeaking it is because she is scared of him. If she turns towards him and stands up, she is being defensive. This is not her trying to stop him from breeding, this her trying to defend herself from his attacks. This will go on for days which is why they should only be introduced for a few hours each day on new bedding until they get used to each other. Squeaking during breeding is not a sign that she is in heat.

If there is blood right now, most likely one of them have wound. If it was internal bleeding the mouse would be dead by now as they have very tiny bodies and not a lot of blood to support those bodies. They should not be bleeding due to breeding. Females of any kind bleed during birth but it is WAY too soon for her to be having babies. You would know if she is pregnant. It is not something mice can easily hide.

Thank you, both. I don't think she has given birth, if she was pregnant when I got her, because she didn't show any physical signs. There are no pinky's or parts of one, so I'm leaning on the side that it was wound. And she's still healthy now so it can't be internal. I checked the same spot and found no blood, so I'm assuming they were fighting, as BCS said. It did look a lot like the male was trying to hump her,but she stood up at some points so maybe she bit him. They both seemed to have calmed down and the male is backing off and they're just cuddled up together now. So I hope within the 16 days they'll mate.

Thanks, guys.